1. Field of the Invention
The present invention relates in general to a stack package and a method for manufacturing the same, which utilizes a Fine-Pitch Ball Grid Semiconductor Package (hereinafter, refereed to as FBGA package). More particularly, the stack package of the present invention has a reduced signal line length and thus an improved electrical property.
2. Background of the Related Art
Generally, semiconductor devices and package technologies thereof have continued to develop with mutual coincidence for high density, high speed, small size and thin thickness. Particularly, package structures have been rapidly advanced from pin insertion type to surface mount type, so that their mounting density in a circuit substrate is increased.
Recently, Chip Scale Packages (hereinafter, referred to as CSP packages) were developed, which maintain properties of a bare chip in a package state intact, are also easy to handle, and have a reduced package size.
Among such various CSP packages, an FBGA package as shown in FIG. 1 currently attracts the highest attention. FIG. 1 is a drawing which shows the general structure of the FBGA package. As shown in FIG. 1, this FBGA package PKG comprises a semiconductor chip 1 on which an electronic circuit is integrated; a circuit substrate 2 for transmitting a signal from the semiconductor chip 1 to the outside; wires 3 for electrically connecting the semiconductor chip 1 to the circuit substrate 2; a molded insulation of resin 5 serving to protect the wires 3; and first solder balls 4 fused to the lower surface of the circuit substrate and serving to output/output a signal from the semiconductor chip 1 to the outside.
Recently, a stack package whose capacity and mounting density are increased by the use of the FBGA package as described above have attracted the attention. Such a stack package comprises unit packages where several unit packages which were individually assembled are stacked on top of each other, unlike a stacked chip package where several unpackaged semiconductor devices are stacked on top of each other. Examples of the stack package according to the prior art are shown in FIGS. 2 and 3.
FIG. 2 is a drawing showing an example of the prior stack package. FIG. 2 shows a stack package which utilizes a Flexible Printed Circuit (FPC) made of a polyimide-based film. This stack package comprises a first package 10A, a second package 10B, and multi-layer films 12 for connecting a signal from the first and second packages 10A and 10B. On the lower surface of the films 12, solder balls 14 are mounted, which serve to transmit a signal to the outside. In this case, all the first and second packages 10A and 10B are the same as the FBGA package shown in FIG. 1.
In a method for manufacturing the stack package as shown in FIG. 2, the second package 10B is attached on the multi-layer films 12, and then subjected to an underfill process so as to fix the solder balls 14 mounted on the second package 10B. Next, both the films 12 are attached on the upper surface of the second package 10B with an adhesive, after which the first package 10A is mounted on the films 12.
However, this stack package has a reliability problem caused by a bonding problem between the polyimide films 12 and the first and second packages 10A and 10B. Furthermore, it is disadvantageous in that, since the polyimide films 12 are assembled in two pieces, processing on assembly is difficult, thereby increasing production costs.
FIG. 3 is a drawing showing another example of the prior stack package. FIG. 3 shows a stack package utilizing a printed circuit board (PCB). This stack package comprises a first package 20A, a second package 20B, a first printed circuit board 22A for connecting a signal from the first package 20A, and a second printed circuit board 22B for connecting a signal from the second package 20B. Also, this package comprises a third printed circuit board 22C which is disposed between the first and second printed circuit boards 22A and 22B so as to connect a signal from the first and second printed circuit boards 22A and 22B. Furthermore, the package has solder balls 24 which are mounted on the lower surface of the second printed circuit board 22B so as to transmit a signal to the outside. In this case, the first and second packages 20A and 20B are also the same as the FBGA package shown in FIG. 1.
In a method of manufacturing the stack package as shown in FIG. 3, the second package 22B is first mounted on the upper surface of the second printed circuit board 22B, and then subjected to an underfill process so as to fix the solder balls. Next, the third printed circuit board 22C are mounted on the second package 22B in such a manner that it can be connected to a signal from the upper parts. Thereafter, the first package 20A mounted on the second printed circuit board 22A is mounted on the resulting structure. On the lower surface of the second printed circuit board 22B, the solder balls 24 are mounted which serve to transmit a signal to the outside.
However, this stack package has problems in that additional costs are spent due to the first, second and third printed circuit boards 22A, 22B and 22C, and also the total height of the package is increased. In addition, it is disadvantageous in that, since the third printed circuit board 22C is disposed in the outside of the first and second printed circuit boards 22A and 22B, the size of the final package is increased.
As a result, this stack package undergoes complex operation processes, and also has a large package structure and a long line length for connecting an electrical signal. Furthermore, in the case of the second package, it causes a problem in terms of heat emission, such that it is difficult to use for high-speed applications.